Along with rapid spreading of multimedia technology in recent years And continuing, memories, for example, magnetic recording media, which play important roles in the multimedia technology, are required to have larger and larger capacity.
In recent years and continuing, remarkable progress has been made to increase the recording density of the magnetic recording media, and the recording density is being increased as fast as by 200% per year. For higher recording density, however, a problem has to be solved regarding the thermal fluctuation in a magnetic film in which magnetic information is recorded. One of the solutions is to form a magnetic recording medium consisting of a recording layer formed from a magnetic material having a high coercivity, and study has been made actively in this field.
As one of the technologies of recording magnetic information in the recording layer formed from the magnetic material having a high coercivity, the so-called thermal assist recording technology has been proposed. In the thermal assist recording, the coercivity Hc of the recording layer (a magnetic material) changes with temperature, and decreases when temperature approaches the Curie temperature Tc. The thermal assist recording technology involves an application of the so-called “Curie temperature recording technology” commonly used in a magneto optical recording device; in the thermal assist recording, a laser is emitted to the recording medium to increase the temperature thereof, and recording is performed by an external magnetic field (recording magnetic field from a magnetic head) with a lowered coercivity.
In this technology, because recording is performed with the coercivity Hc of the recording layer being lowered, it is possible to decrease the recording magnetic field of the magnetic head. Meanwhile, because the coercivity Hc of the recording layer is high at room temperature, it is possible to stably record magnetic information without thermal fluctuation.
When applying the thermal assist recording technology to a magnetic recording device, in addition to the conventional magnetic head for recording and reproduction, it is necessary to add an optical head for emitting a laser. Furthermore, in order that the place to be recorded by the magnetic head is heated by the laser, the technique should be established to precisely locate the optical head relative to the position of the magnetic head during recording.
In the related art, recording with both a magnetic head and an optical head is used in magneto optical recording devices. The positioning method thereof is explained below. In the magneto optical recording device, which performs recording with both a magnetic head and an optical head, first, address signal (pit) formed in grooves on a substrate are read out as optical information, and a positioning mechanism determines the position of the optical head. The magnetic head is mechanically fixed relative to the optical head, and is thereby positioned in compliance with the positioning of the optical head.
When recording on a magneto optical medium, the magnetic field from the magnetic head is applied to a broad region covering the light spot formed on the medium by the optical head. The reason for applying the magnetic field to a broad region is that relative positions of the magnetic head and the optical head cannot be precisely controlled, so the region where the magnetic field is applied is set large so as to be certain to cover the light spot.
That is, with the positioning mechanism used in the magneto optical recording device, the magnetic head is positioned in compliance with the positioning of the optical head, and the magnetic field is applied to a broad region to compensate for the lower positioning precision of the magnetic head relative to the optical head.
In a magnetic recording device, however, the magnetic head can be precisely positioned on the magnetic recording medium by using the servo technique, and it becomes necessary to precisely position the optical head relative to the magnetic head.
Because the surface of the magnetic recording medium is flat without grooves, it is impossible to determine positions using grooves as is done in the case of the magneto optical recording medium. This makes it necessary to study new techniques to precisely position the optical head relative to the magnetic head.
Considering the possibility of mechanically fixing the optical head relative to the magnetic head, converse to the aforesaid magneto optical recording device, this leads to the same result that the positioning precision is bad. If the optical head cannot be positioned precisely relative to the magnetic head, the effect of the thermal assisting by using a laser cannot be produced, and high sensitivity recording in the recording layer, and therefore high density recording, cannot be achieved.